This invention relates in general to gear systems and, more particularly, to an epicyclic gear system.
The typical epicyclic or planetary gear system basically has a sun gear provided with external teeth, a ring gear provided with internal teeth, and several planet gears located between the sun and ring gears and having external teeth which mesh with the teeth on the sun and ring gears. In addition to its gears, the typical system has a carrier to which the planet gears are coupled. Either the sun gear, the ring gear, or the carrier is held fast, while power is delivered to and taken from the remaining two components, and thus power is transferred through the planetary system with a change in angular velocity and an inverse change torque.
The sun and ring gears for all intents and purposes share the same axis—a central axis—while the planet gears revolve about radially offset axes that are parallel to the central axis—or at least they should be. Often the offset axes and the central axis are not parallel, and as a consequence the planet gears skew slightly between sun and ring gears. This causes excessive wear along the teeth of the planet, sun and ring gears, generates friction and heat, and renders the entire system overly noisy.
The problem certainly exists in straddle-designed planetary carriers. With this type of carrier the pins on which the planet gears rotate extend between two carrier flanges in which the pins are anchored at their ends. The carrier experiences torsional wind up which causes one carrier flange to rotate slightly ahead of the other flange. Not only does this skew the pin for each of the planet gears such that one end lies circumferentially ahead of the other end, but it also causes the leading end of the pin to dip toward the central axis and the other end to draw away from the central axis. The end result is a poor mesh between the planet gears and the sun and ring gears, and of course the friction, wear and noise associated with poorly meshed gears. To counteract this tendency, some planetary systems rely on gears that are wider than necessary with lead correction and thus offer greater tolerance to skewing along the gear contact. But these systems can occupy excessive space and can be quite heavy.
Another type of epicyclic gear system uses a single flange carrier and a double cantilever arrangement at the pins for the planetary gears to insure that the planet gears and the sun and ring gears remain properly meshed. In this arrangement the single carrier flange is offset axially from planet gears, and the carrier pins project from that flange into, and indeed through, the planet gears. Each carrier pin has one end anchored in the carrier flange and at its other end is fitted within a sleeve which returns back over the pin, yet is spaced radially from the pin, to support the planet gear. U.S. Pat. No. 3,303,713 to R. J. Hicks shows a double cantilevered arrangement. Sometimes an antifriction bearing is fitted between the sleeve and the planet gear. But antifriction bearings consume space, making the planet gears excessively large in diameter, which in turn makes the entire gear system too large and heavy.